Traditional Chinese medicine (TCM) is one of the oldest and most widely used indigenous medical systems in the world. It is difficult to effectively practice or evaluate TCM outside of its core framework, which includes a diagnostic system that is more conceptual and less technologically driven than that of conventional medicine. TCM diagnosis relies entirely on clinical symptoms and signs that are discerned by the practitioner. Thus far, the inter-practitioner reliability of TCM diagnoses and treatment plans have not been investigated. The establishment of diagnostic and prescriptive consistency is crucial for efficacy studies involving individualized treatments within the TCM framework. This study aims to examine the consistency of TCM diagnoses and herbal prescriptions under controlled conditions. Rheumatoid arthritis (RA) patients will be individually evaluated by three TCM practitioners; the diagnostic and prescriptive behaviors of the practitioners will be recorded and analyzed to determine: 1) The extent to which two or more TCM practitioners assign comparable TCM diagnoses to the same RA patients; 2) The extent to which two or more TCM practitioners prescribe comparable herbal formulas to the same RA patients; and 3) The extent to which TCM diagnoses are related to conventional medical clinical assessments and biomedical tests of RA. Variables that cause inconsistency will be identified and analyzed. The information obtained from this study is essential for the design of clinical trials examining the efficacy TCM in the treatment of RA. More importantly, this study will be broadly applicable to clinical TCM research in general, and may help to establish a stronger methodological model for the evaluation of individualized treatment.